The invention relates to a speed-adaptive dynamic-vibration absorber for a shaft rotatable about an axis, including a hub part on which at least one inertial mass is provided. The inertial mass, starting from a middle position in the distance from its center of gravity to the axis is at a maximum, is moveable back and forth relative to the hub part along a path of motion in deflection positions such that the distance of the center of gravity of the at least one inertial mass changes with respect to the middle position.
Such a speed-adaptive dynamic-vibration absorber is described in the German Patent 196 31 989 C1.
At shafts of periodically operating machines, e.g., at the crank shaft of an internal combustion engine, torsional vibrations occur which are superimposed on the rotational motion, the frequency of the torsional vibrations changing with the rotational speed of the shaft. To reduce these torsional vibrations, dynamic-vibration absorbers can be provided. They are described as speed-adaptive when they can cancel torsional vibrations over a larger speed range, ideally over the entire speed range of the machine. The principle underlying torsional vibration cancellers is that, due to centrifugal force, the inertial masses endeavor to circle the axis at the greatest distance possible when a rotary motion is initiated. Torsional vibrations which are superimposed on the rotary motion lead to a pendulum-like relative movement of the inertial masses. The dynamic-vibration absorber has a natural frequency fabsorber proportional to the rotational speed, so that torsional vibrations having frequencies which are proportional in the same manner to the shaft rotational speed n (in revolutions per second), can be canceled over a large speed range. Expressed mathematically, fabsorber=x*n where x is the order of the exciting vibration. For example, in the case of a four-cylinder four-stroke engine, this has the value x=2. In the known dynamic-vibration absorber, the inertial masses move relative to the hub part in a purely translatory manner on circular paths of motion. However, the known speed-adaptive dynamic-vibration absorber has the disadvantage that it is still not possible, to achieve optimum canceling effectiveness over the entire speed range and load range.
The object of the present invention is to attain improved canceling effectiveness over a wide speed range and load range.
This objective is achieved in a speed-adaptive dynamic-vibration absorber of the type indicated above, in that the path of motion has a radius of curvature which changes at least section-by-section with increasing deflection of the inertial mass out of the middle position.
This design according to the invention permits improved canceling effectiveness. At the same time, the speed-adaptive dynamic-vibration absorber can be better adapted to the torsional vibrations to be canceled. The teaching of the present invention opens up a great, previously unknown leeway in the design of the dynamic-vibration absorber, permitting considerable improvement in absorbing dynamic vibrations.
Particularly effective absorption of dynamic vibrations is achieved, in that the radius of curvature decreases at least section-by-section with increasing deflection of the inertial mass out of the middle position.
According to one particularly advantageous refinement, the radius of curvature decreases continuously. In this manner, the path of motion receives a curvature which can be represented by a strictly monotonically increasing function.
Particularly effective dynamic-vibration absorption is also attained by providing a plurality of inertial masses adjacent in the circumferential direction.
Particularly large inertial masses can be provided on a small installation space if the inertial masses, adjacent in the circumferential direction, are rounded off at the ends facing one another, and are loosely in contact with one another, regardless of the deflection.
Further improvement is achieved, in that the radius of curvature of the path of motion in the middle position is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where L is the distance of the curvature midpoint from the axis, x is the order of the exciting vibration and k is a factor in the range from 0.8 to 1.2. In this context, the curvature midpoint represents the point of rotation of the inertial mass. The order x of the exciting vibration indicates the relationship between the vibrational frequency and the rotational speed (in revolutions per second). For example, in the case of a four-cylinder, four-stroke engine, x=2 is for the dominantly exciting firing order. Optimized vibrational damping can be achieved under the most varied conditions by varying k in the indicated range.
Advantageously, k lies in the range from 0.8 to 0.999 or 1.001 to 1.2.
Vibrational damping can be further improved by providing the path of motion with the shape of a cycloid section. A cycloid is a curve which develops when a circle rolls along on a straight line. A point fixedly joined to the circle at a distance from its midpoint describes a curve, composed of congruent pieces, as the circle rolls along on the straight line.
The tuneability of the dynamic-vibration absorber is further improved, in that the path of motion lies in a field which is bounded on the one hand by a circle whose radius of curvature is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=1.2, and on the other hand by a cycloid whose radius of curvature in the middle position is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=0.8. In this context, the circle and the cycloid are arranged in such a way that their paths coincide in the middle position. Good dynamic-vibration absorption can be attained by this arrangement of the paths of motion of the inertial masses located in a centrifugal force field. In this manner, it is possible to achieve a deflection-independent duration of the pendulum swing of the inertial masses that are moveable relative to the hub part. Thus, for example, in addition to the non-linearity of the swinging inertial masses, hydrostatic and hydrodynamic effects resulting from a lubricant can also be largely compensated.
In addition, the path of motion in a first section adjacent to the middle position can lie in a first region of the field, the first region being bounded on one hand by a circle whose radius of curvature is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=1.0, and on the other hand by the circle whose radius of curvature is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=1.2. At the same time, the circles are arranged in such a way that their paths coincide in the middle position.
According to a further aspect of this inventive idea, the path of motion in a second section, which is adjacent to the first section, lies in a second region of the field, the second region being bounded on one hand by the circle whose radius of curvature is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=1.0, and on the other hand by the cycloid whose radius of curvature in the middle position is determined by the formula       R    =          k      ⁢              L                  x          2                      ,
where k=0.8. The circle and the cycloid are arranged in such a way that their paths coincide in the middle position. This design of the path of motion, which is different region-by-region, opens up new possibilities for further optimizing the damping under the most varied conditions.
According to one advantageous refinement of the invention, the at least one inertial mass is supported in the hub part by axially parallel bolts that are rotatable about a bolt axis, the bolts being allocated to first rolling paths (i.e., rolling curves)of the hub part and second rolling paths of the inertial mass.
In a further embodiment based on this invention, given an identical formation of the rolling paths of the inertial mass and the hub part, a point exists, allocated to the inertial mass, which shifts with the inertial mass along the path of motion, and whose distance in the middle position of the inertial mass is twice as great from the curvature midpoint, allocated to the middle position, of the path of motion of the point as the distance of the point from the bolt axis. The first and second rolling paths are designed in such a way that, in each deflection position, the bolt axis is located on the geometric center of an imaginary connecting line between the curvature midpoint, allocated to the middle position, and each point of the path of motion of the point. By this means, it is specified how the rolling paths upon which the bolts roll are to be constructed in order to achieve good vibrational damping.